One of the major cardiovascular problems afflicting human beings is the build-up of plague on the inside of blood vessel walls. This narrows the passage for blood and, in more extreme cases, even closes it off entirely.
One of the common treatments is the use of angioplasty. In this method, an inflatable balloon on the end of a catheter is inserted into the blood vessel and inflated at the point of plaque build-up, thereby dilating the artery or vein. However, this procedure provides only temporary relief. The blood vessel tends to return to its original condition within a relatively short period.
To overcome this problem, the procedure has been modified to include the use of a mesh-type metal stent. The stent is crimped around the balloon portion of the catheter and inserted into the blood vessel along with it. The stent has sufficient yieldability so that, when the balloon is inflated, the stent is expanded (see FIG. 1) into contact with the blood vessel walls. The balloon is then deflated and removed, leaving the stent in place. This is a definite improvement over the prior procedure, but is by no means completely satisfactory. In actuality, about 25% to 30% of such stents occlude within six months. This is the result of cellular proliferation whereby the cells grow through the spaces in the grid of the stent, thus developing the blockage anew.